This invention relates to helm steering systems and, in particular, to multiple helm steer-by-wire steering systems for marine craft or other vehicles.
Conventional marine steering systems couple one or more helms to one or more rudders utilizing mechanical or hydraulic means. In smaller marine craft, cables conventionally have been used to operatively connect a helm to the rudder. Alternatively the helm has been provided with a manual hydraulic pump operated by rotation of the steering wheel. Hydraulic lines connect the helm pump to a hydraulic actuator connected to the rudder. Some marine steering systems provide a power assist via an engine driven hydraulic pump, similar to the hydraulic power steering systems found in automobiles. In those systems a cable helm or a hydraulic helm mechanically controls the valve of a hydraulic assist cylinder.
It has been recognized that so-called steer-by-wire steering systems potentially offer significant advantages for marine applications. Such systems may yield reduced costs, potentially more reliable operation, more responsive steering, greater tailored steering comfort, and simplified installation. Smart helms allow an original equipment manufacturer (OEM) to tailor steering feel and response to craft type and operator demographics. Steer-by-wire steering systems are also better adapted for modern marine craft fitted with CAN buses or similar communications buses and may make use of electrical information from speed, load and navigation, autopilot or anti-theft devices for example.
Various attempts have been made to provide a commercially viable steer-by-wire steering system for marine craft. An example is found in U.S. Pat. No. 6,273,771 to Buckley et al. which utilizes a CAN bus for a plurality of helms. Another is found in U.S. Pat. No. 5,107,424 to Bird et al. A further example is found in U.S. Pat. No. 6,311,634 to Ford et al.
However these earlier systems have not been completely successful in replacing more conventional hydraulic steering systems in multiple helm marine craft for example. Accordingly there is a need for an improved steer-by-wire steering system particularly adapted for multiple helm marine craft and also potentially useful for other steering applications such as tractors, forklifts and automobiles.